They're not exactly any more difficult to code than the hero cards are. Almost all the hero cards have a new ability, just like these spell cards do. That's what makes them interesting.
I don't want to get into a debate about hero cards; overall I like them, but my cards are just simply cards. Your hero cards being able to only have one in the deck and only one on the board makes them complicated. The way to get them is complicated; mine would only need to be bought
![Tongue :P](https://elementscommunity.org/forum/Smileys/solosmileys/tongue.gif)
. And some of the cards abilities are complicated. Vampire Lord, Bazuul, and Rocky's abilities, for instance, are pretty complicated, but they're still good cards.
Just because a card is complicated doesn't mean it's bad. In fact, arguably the best cards in the game are pretty complicated (Sundial, Animate Weapon...).
The message could be something "Changes every aspect of targeted creature to dark, and destroys light creatures"
And as do the balance of Quantum Freeze, I'm not going to debate costs, because I really should have left the costs blank. Zanz should be the one to decide on balance; he knows the game better than anyone.